Agronomic benefits of alfalfa mulch applied to organically managed spring wheat

Field experiments were established at two locations in Manitoba in 2002 and 2003 to determine N contribution, moisture conservation, and weed suppression by alfalfa mulch applied to spring wheat (Triticum aestivum L). Mulch treatments included mulch rate (amount harvested from an area 0.5×, 1× and 2× the wheat plot area), and mulch application timing (at wheat emergence or at three-leaf stage). Positive relationships were observed between mulch rate and wheat N uptake, grain yield, and grain protein concentration. At Winnipeg, the 2× mulch rates (3.9 to 5.2 t ha-1) produced grain yields equivalent to where 20 and 60 kg ha-1 of ammonium nitrate-N was applied in 2002 and 2003, respectively. Where mulch and ammonium nitrate produced equivalent grain yield, grain protein in mulch treatments was often higher than where chemical fertilizer was used. N uptake was also observed in the following oat (Avena sativa L.) crop. The highest mulch rate (2×) produced higher N uptake and grain yield of second-year oat compared with ammonium nitrate treatments. N use efficiency of mulch-supplied N by two crops over 2 yr [calculated as (treatment N uptake – control N uptake)/total N added] was between 11 and 68%. Mulch usually suppressed annual weeds, with greater suppression with late- than early-applied mulch. Increased soil moisture conservation was observed with high mulch rates (≥ 4.3 t ha-1) at three sites. Alfalfa mulch holds promise for low-input cropping systems when used on wheat at the 2× rates. Key words: Legume N, low-input farming, integrated weed management, wheat protein